1. Field of the Invention
This invention relates to the field of mining and/or extraction of bitumen or heavy oil deposits which are found in nature associated with foreign matter, such as sand particles, various types of stone and clay.
A related field is that of the wearing away of materials into relatively small particles by a softening and/or abrasion process using a low temperature freezing fluid which may contain abrasion particles to accelerate the process.
2. Description of Prior Art
Bitumen (heavy oil) deposits from which synthetic crude oil can be formed occur in nature in deposits which contain bitumen associated with foreign matter; such as sand particles, various types of stone and clay. An example of such a deposit which is currently being exploited commercially is that of the Athabaska tar sands located in Alberta, Canada.
Information regarding a description of this deposit, current procedures used in extracting the tar sands, delivering them to a refinery, separating bitumen from foreign matter and then upgrading bitumen into synthetic crude oil is contained in the Autumn 1967 issue of OUR SUN, magazine of the Sun Company. Used with permission of the Sun Company.
As noted in the above magazine, the Athabaska tar sands constitute one of the world's largest single energy resource and are believed to contain over 600 billion barrels of synthetic crude oil of which it is estimated half can be recovered through existing techniques of production.
The current procedures used in extracting the tar sands, delivering them to a refinery and then separating bitumen from foreign matter have a number of significant problems that this invention is designed to overcome. For example, the prior art employs giant excavators equipped with rotating bucketwheels to extract the tar sands from the deposit. The digging wheel on an excavator (there are two of them) has ten buckets, each bucket equipped with teeth and capable of biting out and holding nearly two tons of sand. Some of the problems encountered using current procedures are described in a newspaper article titled "The Oil is Synthetic, but the Problems are Real," Oct. 12, 1975. Bus. and Fin. Sect. "Copyright 1975 by The New York Times Company. Reprinted by permission" wherein it is stated "A major part of the problem is the changing nature of the oil sands, which are impossible to stockpile. In summer, they are like an asphalt road mix and in the early days they wore out bucketwheel teeth in four hours. In winter, at 50 degrees below zero, the tar sands are hard as carborundum, and the bucketwheel teeth have glowed red in frustration. The tar sands rip conveyor belts, corrode process units and make vehicle maintenance a nightmare". Because of the above-noted problems, the theoretical capacity of a bucketwheel excavator for extracting tar sands is reduced from a theoretical maximum of 215,000 tons a day to an average of 108,000 tons a day.
Another disadvantageous feature of the prior art is that separation of bitumen from foreign matter does not occur at the deposit (on site). Instead, the tar sands, as extracted, are transported by conveyor belts to the refinery, despite the fact as noted in the above-mentioned magazine that from about 42.5 million tons of tar sands only perhaps 21 million barrels of bitumen will be recovered. The remaining materials transported to the refinery at considerable expense must now be transported again from the refinery to a tailings pond where they are discarded.
Additionally, the problem concerning ripping of conveyor belts noted in the above-mentioned article will get worse in time as the distance from the deposit being worked recedes from the refinery and either longer or additional conveyor belts are required.
Furthermore, additional problems are encountered using the present method in separating bitumen from its foreign matter at the refinery and in obtaining maximum recovery of bitumen. As described in the above-mentioned magazine published by the Sun Company, at the refinery the tar sands are supplied first to one of a number of conditioning drums. While the drum rotates slowly, water heated to a temperature of about 190.degree. F. and steam are added, mixing bitumen, sand, water and steam into a pulp. From the drum, pulp is piped to one of a number of double-walled separation tanks. Here, bitumen extracted from the sand rises to the surface as a froth and is swept between the inner and outer walls to be collected.
Sand and water fall to the bottom of the separation tank and are piped to the tailings pond. There is no sharp dividing line between the frothy bitumen and the pulp below. Between the froth on top and the sand and water on bottom are the "middlings", containing clay, bitumen and water. Middlings are pumped to scavenger cells where air is forced in, causing the remaining bitumen to froth to the surface. Again froth is recovered, while sand and water ae pumped to scavenger cells where the same process recurs. Between them, separation and scavenger cells allow the extraction plant to recover up to 90 percent of the bitumen from the sand.
The above-noted difficulties in separation and recovery of bitumen and the apparently involved, time consuming, elaborate equipment required to effect this separation and recovery are attributed by the inventor to the following.
a. The relatively large chunks of tar sands extracted from the deposit by the bucketwheel teeth and supplied to a conditioning drum.
b. The difficulty within a conditioning drum is breaking down these relatively large chunks into individual prticles of bitumen uncontaminated by foreign matter and visa versa within the practical allotted time that the pulp is permitted to remain in a conditioning drum.
c. Because of the difficulty noted in b. above, there is formed inside a separation tank a "middling" layer which is believed to consist of relatively small pieces of deposit which contain varying amounts of bitumen and foreign matter. These pieces can run the entire gamut and can contain from between 100 percent to 0 percent bitumen, the remainder being foreign matter of variable density depending upon composition. Thus, they have a specific gravity ranging from that of bitumen to that of foreign matter and consequently form the "middling" layer there-between.
d. The relatively small difference between the specific gravities of bitumen, sand, foreign matter and water inside a separation tank, thereby making gravity separation into the respective components a slow tedious operation. This situation is complicated further by the fact that bitumen normally has a specific gravity greater than that of water. Thus, frothing to reduce the specific gravity of bitumen is a necessity so that it will float on top of water, thereby facilitating its separation from the other components. Those particles of bitumen not affected by frothing sink into the middling layer and require additional costly operations to effect their recovery.